The present invention relates to a top pole support for aerial electric power lines, in particular with suspended wires, in which the aerial electric power lines include at least three wires and the top pole support has insulating means, in particular suspended insulating means, to support the wires.
Aerial electric power lines for medium and high voltage, as known, are supported by suitable poles that have variety of top pole supports, i.e., supports to hold the wires of the aerial electric power lines.
The top pole supports are usually formed by a structure of straight bars, like cantilevers or a trellis, i.e., to which insulators or chains of insulators are connected to support the wires.
Medium voltage lines, in the past, used to be mounted on the top pole support via stiff insulators that were less resistant to mechanical and electrical stress than suspended insulators, i.e., hanging from the top pole support.
In order to convert lines with stiff insulators into lines with suspended insulators, it is necessary to substitute for the top pole support, one that should have the following features:                It has to support the wires at a height such that the wires are not very low along the span;        It must have an open structure in order to nest the central wire without having to cut and then splice that wire;        
In FIG. 1, a top pole support 10 according to the prior art is shown mounted on the top of a pole 11, and has four arms 12a, 12b, 12c, 12d, i.e., the above mentioned straight bars. The two arms 12a and 12b perpendicularly protrude from the pole 11, in opposite directions, while arms 12c and 12d protrude in oblique directions above the pole 11, symmetrically with respect to the axis of the pole 11. Each of the four arms 12 has on its distal extremity with respect to pole 11, a chain of suspended insulators 13, to which corresponding wires 14 of the electrical aerial lines are hooked. Each of arms 12a and 12b has a chain of insulators 13 that extends downward vertically and carries a wire 14. Arms 12c and 12d have small beams 15 to which corresponding chains of insulators 13, that together support the third wire 14, are connected.
Supports known in the prior art, like the one shown in FIG. 1, have several drawbacks attributable to substantial weight and cost of the structure, that is further disadvantageously constituted by several pieces which must be assembled on the pole.
Moreover the “V” shaped chains associated to the arms 12c and 12d are too heavy and they do not stretch completely when used with the lighter wires.
Another drawback of the known supports resides in the necessity to distance insulator chains at the same height with respect to each other sufficiently to comply with specifications regarding distance between wires in the span in the presence of wind.
Also, vertical alignment of the insulator chains has to be avoided, since the formation of icicles on the wires during wintertime and their subsequent detachment provokes whip lash reactions that could short circuit two wires disposed one above the other.
The operation of changing the top pole support can be performed with the line power turned off. However, it is often more convenient to operate with voltage applied in order not to interrupt service to users. The operation of changing the top pole support requires a top pole support with a structure that allows replacement by simple and safe operations that can be performed by workers at predetermined safe distances from the wires.